1. Field of the Invention
The present invention relates to an image pickup apparatus having a photoelectric conversion function.
2. Related Background Art
FIG. 11 is a block diagram showing an example of an autofocus (AF) sensor circuit for multipoint distance measurement which is used in a conventional single-lens reflex camera. An AF sensor using this AF sensor circuit was published by the inventors of this application in the Institute of Image Information and Television Engineers Technical Report Vol. 25, No. 28, pp. 1 to 6, March 2001. In FIG. 11, reference numeral 900 denotes a semiconductor chip (semiconductor substrate); 901, an AF sensor circuit block; 902, an analog circuit block; and 903, a digital circuit block.
In this AF sensor, the AF sensor circuit block 901 is composed of eight linear sensor circuits 1A (1B) to 8A (8B) to enable seven-point distance measurement (cross distance measurement in the center). The analog circuit block 902 is composed of AGC circuits 1 to 8 for controlling accumulation time of each linear sensor circuit, a signal amplifying circuit 902A for amplifying a signal from the AF sensor circuit block 902 to output the signal, a band gap circuit (reference voltage generation circuit) 902B for generating a reference voltage, and an intermediate voltage generation circuit 902C for generating voltages required in sensor circuits and analog circuits.
The digital circuit block 903 consists of an input/output communication circuit (I/O) for communicating with a microcomputer, a timing generator circuit (T/G) for generating a drive pulse of a sensor, and a multiplexer circuit (MPX) for selecting various analog signals. Since high-speed autofocus is required in a single-lens reflex camera, an AF sensor realizes a high-speed operation by driving the eight linear sensor circuits and the AGC circuits in parallel.
However, in the above-mentioned conventional autofocus sensor, current consumption in operation is increased by driving each circuit simultaneously. Although a significant problem is not caused in a single-lens reflex camera because a battery with a large current capacity can be mounted thereon, since only a battery with a small current capacity can be mounted on a compact camera, a battery life of the compact camera is extremely reduced.
In addition, AE and AF in the compact camera are those of an external measurement system unlike a TTL system of the single-lens reflex camera. Thus, an unnecessary AF sensor circuit may operate depending upon a zoom range of a photographing lens used in the compact camera (a distance measurement point of an AF sensor is located outside a photographing range).